The overall goal of this project is to understand the structure and function of highly functional membranes using a combination of genetic, molecular and photosynthetic techniques. In an attempt to dissect the complex photosynthetic membranes of the blue-green alga, Synechococcus cedrorum, we are using two specific approaches. In the first, we have isolated temperature-sensitive mutations defective in photosynthesis. These mutant strains have aberrations in one or more of the following properties: fluorescence kinetics, low-temperature fluorescence spectra, growth kinetics oxygen evolution and protein composition. The mutants so far characterized seem to have perturbations in the structure of the membrane which lead to functional abnormalities. The second approach utilizes cellular functionation and isolation of purified membrane fragments containing either Photosystem I (PSI) or PS II. The isolation procedure consists of cell breakage, treatment with 0.5% digitonin, centrifugation on 5-30% sucrose gradients, and chromatography on DEAE-cellulose. Highly purified photosystem preparations have been obtained; characterization of these preparations is not in progress. Both of these procedures are being used to study membrane architecture of the blue-green algae and its relation to photosynthetic function. BIBLIOGRAPHIC REFERENCES: Sherman, L.A. and Connelly, M. (1976). Isolation and Characterization of a Cyanophage Infecting the Unicellular Blue-green algae. A. nidulans and S. cedrorum. Virology 72, 540-544. Sherman, L.A. and Cunningham, J. (1977). Isolation and Characterization of Temperature-Sensitive, High-Fluorescence Mutations of the Blue-green Alga, Synechococcus cedrorum. Plant Science Letters, in press.